Common problems and solutions of central air conditioning water system
First, the air conditioning water system is blocked.
Pipe blockage is the most common problem in air conditioning system, which often causes the system to fail to work normally. The main reasons for the blockage are:
1) foreign body entry
During the debugging of a central air conditioning system in our library, it was found that the rubber soft joint at the inlet of the cooling water pump was sunken and cracked, which was thought by the construction unit to be caused by insufficient pump head and negative pressure in front of the pump. However, when the water filter in front of the pump was opened, it was found that the filter was seriously blocked, resulting in negative pressure in front of the pump and the cooling water pump could not work normally. After clearing the blockage, the motor current returned to normal and the cooling pump operated normally. Similarly, when I was working in a hotel, I found that the cooling effect of a conference room was very poor. Although the valves in front of the air-conditioning fans in return pipe are all open, the pressure gauge of the air-conditioning fans in return pipe shows close to zero, so it is concluded that the flow of the cooling plate of the air-conditioning fans is extremely small, and it is estimated that the pipes are blocked. When I turned on the water filter in front of the air-conditioning fan in return pipe, I found that the blockage was very serious, with pebbles, construction hemp and bolts. After the blockage was removed, the room cooling situation was immediately improved.
2) The water quality is poor, resulting in scale and rust.
The water in the central air-conditioning pipe network is generally ion softened, and the pipes are all stainless steel pipes, so they are relatively pure. It is worth noting that in most cases, the cooling water used to cool the condenser is mostly ordinary tap water, and it is mostly open circulation. Even if the water quality is good and the cooling water is recycled for a long time, under the influence of temperature, flow and evaporation, the water will change as follows:
(1) The increase of water temperature promotes the decomposition of bicarbonate in water, in which carbonate ions and calcium ions in water form scale.
(2) The cooling water is recycled and continuously evaporated and concentrated, so that the salt content in the water increases and the PH value increases. The data show that the PH value of cooling water with PH value of 6~8 can reach about 20 after one month's use, which accelerates the formation of scale.
(3) The cooling water fully contacts the air, so that the concentration of dissolved oxygen in the water increases to saturation, and Fe(OH)3 scale or Fe2O3 precipitate is generated, which causes corrosion to the pipeline, coarsens the pipe wall and accelerates the generation of scale.
The formation of scale not only reduces the heat transfer effect and effective pipe diameter, but also causes a large amount of scale to fall off and gather at the filter, causing blockage. The descaling methods include oil mechanical method, chemical method and high frequency electromagnetic descaling. Mechanical method and chemical method have been widely used, but both methods are harmful to equipment and chemical method pollutes the environment. Therefore, high-frequency electromagnetic descaling is gradually adopted. Electronic descaler uses electronic components to generate high-frequency electromagnetism, which reduces the potential of water molecules and weakens the electrostatic attraction between dissolved salt ions and charged ions, making it difficult to gather. Our library uses an electronic descaler produced by a factory in Beijing. After four years of use, no scaling phenomenon was found in the cooling water pipe.
3) Propagation of algae and fungi
Cooling water has the following conditions, which are easy for algae and fungi to reproduce:
Water temperature. Generally, the temperature of cooling water is about 40℃, which is beneficial to the reproduction of algae and fungi.
Cooling water is mostly in open circulation, so it is easy for dust and sundries to enter and bring a lot of dust buds.
The contact of cooling water with air is rich in oxygen and contains a lot of inorganic salts, which is beneficial to the growth of algae and fungi.
Algicides can be used to kill algae in cooling water. Algicides are generally toxic and harmful to the environment and human body. After installing electronic descaler in the cooling water pipeline of our library, water molecules are excited by high-frequency alternating electromagnetic field to rupture the microbial cell wall, thus achieving the effect of descaling and sterilization and algae elimination.
As can be seen from the above example, the cleanliness of the air conditioning water system pipeline is directly related to whether the air conditioning system can work normally. Therefore, the following work needs to be done:
First of all, a relatively large drain valve should be installed at the bottom of the system pipe network. The valve is too small, the pollution discharge effect is poor, and the cleaning times are many. If it is not at the bottom, the sewage discharge will not be complete.
A manual exhaust valve should be set at the top of the pipe network, which should be opened when water is injected and emptied as soon as possible after it is filled. The number of cleaning depends on the size and cleanliness of the pipe network, ranging from a dozen or even dozens to several times.
If the sewage outlet is located in the basement, full consideration should be given to whether the sewage can be discharged quickly.
After the cleaning work is completed, it is necessary to carry out the trial operation of the water system circulation, with the aim of flushing the dirt and sediment in the system.
The most important sign to judge whether the decontamination device is blocked is to observe the running current of the circulating water pump. The more the current drops, the more serious the blockage is. In addition, the blockage of the decontamination device can also be judged according to the flowmeter and the inlet and outlet pressure gauges. According to their respective ratings, the less the flowmeter reading, the lower the outlet pressure and the more serious the blockage.
Second, the choice of water pump
In air conditioning system, the choice of water pump is very important. At present, more and more manufacturers produce pumps, and the actual performance of pumps produced by some manufacturers can not meet the nameplate parameter standard, which will lead to the system not working normally.
In practical work, pump selection should meet the requirements of practicality and economy. First of all, when choosing the type of pump, it is necessary to make clear the nature of the liquid to be transported, so as to choose different types of pumps. Secondly, water pumps are mainly divided into centrifugal type, mixed flow type and axial flow type, and according to the working type, they are divided into three types: variable current, variable voltage and constant voltage. The structure of the pump should be selected according to the head, flow and efficiency. Thirdly, according to the maximum flow and lift required by the system, the safety margin of 10%~20% is increased to ensure the stability and economy of operation.
The power of water pump motor can be calculated according to the following formula
P 1=KQH/6. 1 1η
formula
P 1- pump motor power
Q- water flow (m3/min)
H- total lift (m)
η-total efficiency
K- margin coefficient (usually 1.05~ 1.2)
We have encountered such a situation in a certain unit. There are two refrigeration units and two water pumps in the air conditioning room, but at the same time, only one refrigeration unit and one water pump can work normally in the whole system. If two refrigeration units are started at the same time, the farther refrigeration unit will automatically stop. As only half of the chillers are put into operation, the effect of air conditioning is very poor. It is judged that the actual performance of the water pump equipped with refrigeration unit can not reach the nameplate parameters. When two units are working, the flow is insufficient, and the flow protection device stops the chiller. When a unit works, the system resistance is small, and there is no phenomenon of insufficient flow. Therefore, it is recommended that the owner replace the water pump. After that, the two units can work normally at the same time.
The lithium bromide direct-fired air-conditioning unit in Xi 'an Library is equipped with two 75kwSLS single-stage single-suction vertical centrifugal cooling pumps and two 45kwSLS single-stage single-suction vertical cold heat pumps, 1 user 1 standby, all of which are produced by Shanghai Liancheng Pump Manufacturing Co., Ltd., with compact structure, small volume, stable operation, low noise, no leakage and convenient maintenance.
For the running water system, some still need to solve the problem of excessive pump selection. Because there is a 20% margin in the selection of flow and lift, and there is also a 20% margin in the selection of motor, sometimes the flow and lift greatly exceed the required value, so it is necessary to turn down the valve to throttle, which reduces efficiency and wastes a lot of energy. Two methods can be adopted, one is to replace the appropriate water pump and motor during the maintenance of the water pump, and the other is to install a variable frequency speed regulating device for the water pump, because the water pump and fan are both secondary equipment, namely
T=Kn2
Where t- torque k- coefficient n- speed.
That is to say, when the rotational speed is reduced to 1/2, the torque is reduced to 1/4, and the power is reduced to 1/8, there is great potential for energy saving in water pump speed regulation. The speed regulation modes of asynchronous squirrel-cage motor are: hydraulic slip clutch, hydraulic coupling, electromagnetic slip clutch and frequency conversion governor, among which the frequency conversion governor has high efficiency, good performance and saves electric energy, and the transformation investment can be recovered in 2~3 years. In addition, the variable frequency governor can realize the soft start of the pump, eliminate the impact of the starting current of the pump on the power grid, reduce the impact of the starting torque on the mechanical part of the pump, and realize the impact of the water hammer effect on the pipe network. [Note] This method has been adopted for the hot water pump of Zhiyuan Hotel.
Third, the problem of expansion tank.
In order to ensure the normal operation of the air conditioning system, it is necessary to maintain a stable hydraulic condition. Therefore, the water supply pipe of the expansion tank should be larger than the conventional design. For the direct-fired lithium bromide unit, if the power is suddenly cut off during operation, neither the chilled water pump nor the cooling water pump will work, but the concentration of lithium bromide solution is still high and continues to be absorbed. In the process of absorption and cooling, the cold generated by the evaporator cannot be taken away, which may lead to crystallization of the solution. In practical work, if this happens, it is necessary to use the water volume and pressure of the water system to open the manual regulating valve to take away the cold energy of the refrigeration system and the heat energy of the cooling system of the lithium bromide main engine, so as to achieve the purpose of protecting the unit.
The cold and warm water system of Xi 'an Library adopts ZRL series automatic water softener developed and produced by Xi 'an 623 Research Institute to make soft water, and adopts closed cycle. Its constant pressure mode is high expansion water tank constant pressure, and it is equipped with photoelectric water level gauge. The high water level is 0/00 cm from the overflow/kloc-,the low water level is 200cm from the bottom, and the middle water level is 500cm from the bottom. When the water level reaches the low level, the water level gauge sends a signal to start the make-up pump; when the water level reaches the high level, the make-up pump stops, and two make-up pumps are in use and one is for standby. The cooling water system is open circulation, and the electronic water treatment instrument is used to treat the cooling water.
The expansion pipe of the expansion tank must be connected to the bottom of the chilled water system. In this way, the air in the terminal equipment can be exhausted at one time in a bottom-up way, and the water supply speed is also fast. However, in the actual installation process, because the elevation of the conventional expansion tank is slightly higher than the top of the chilled water system, the distance from the outlet pipe of the expansion tank to the top of the chilled water system is only a few meters, while the distance to the bottom of the chilled water system is generally more than tens of meters, and more pipes and fittings are used, which increases the cost. Therefore, some construction units often connect the expansion pipe to the top of the nearby chilled water system, so that the make-up water changes from top to bottom, which will lead to the air accumulated in the fan coil of the air conditioning system can not be discharged.
Fourthly, the problem of cooling towers.
The lithium bromide direct-fired machine in Xi 'an Library adopts YLT—600 square tower with high efficiency and low noise, and the cooling tower fan can be independently controlled and linked with the water chiller. According to the working conditions, the cooling effect of the cooling tower is mainly related to the exhaust air volume. In order to maintain and improve the exhaust volume of the fan, we have taken the following measures:
Oil the motor bearing of the cooling tower regularly (April and May before the cooling season every year). Observe the running current to make it run within the rated range. At the same time, change the gear oil in the reducer every month to ensure the normal operation of the cooling tower motor and its reducer.
Adjust the angles of the fan and blades to make them consistent.
The cooling tower is installed outdoors, and the environment is humid. Although the motor is closed, the junction box should be waterproof, the terminal should be fastened and properly coated with grease (commonly known as butter).
The socket is blocked with waterproof glue, and the wire is tied to the threading pipe with plastic tape to prevent water from entering.
The rubber pad of junction box is easy to age and needs to be replaced every year.
Grease the gap between the junction box and the fixing bolt to prevent it from opening due to rust in the next overhaul.
Regularly check the insulation resistance of the motor to the ground. It can be used when the insulation resistance is greater than 0.5mΩ according to regulations, but attention should be paid to replacement and heating. If the previous value is 2mω, you should pay attention to it if it suddenly drops to 1mω.
We also noticed in our work practice that the temperature of cooling water is only about 22℃ when we start the machine for the first time every day, and the ambient temperature is also low. The refrigeration unit has small load, low condenser temperature and poor absorption effect. Therefore, the cooling tower fan should be turned on about 15 minutes after the main engine is turned on, when the cooling water temperature rises to about 30℃.
The cooling effect of the cooling tower is also related to the speed of the water distributor, whether the water distribution is uniform and whether the water distribution holes are blocked. Adjusting the rotating speed of the water distributor is mainly realized by adjusting the water spraying angle of the water distributor and cleaning the bearing of the water distributor. Generally, the rotating speed of water distributor should reach 8- 12 rpm, not less than 6 rpm, and the water quantity should be controlled within the rated range of 15%. In addition, the cooling effect of the cooling tower is also related to the size of the cooling tower itself. If the height of the tower is not enough, the ventilation time in the cooling tower is short and the cooling effect is poor. Secondly, it is absolutely forbidden to have oil in the cooling tower, because the oil will enter the condenser with the cooling water and adhere to the copper tube wall, resulting in oil film thermal resistance and affecting the heat exchange effect.